KABUL, Afghanistan
-- An explosion hit the eastern part of the Afghan capital and killed two civilian contractors working for the U.S.-led international military coalition on Monday.

A statement released by the coalition, known as ISAF, confirmed that two people were killed by a "vehicle-borne improvised explosive device attack."

An Afghan official at the scene told CBS News’
Mukhtar Ahmad that the attack had targeted foreign military forces, but ISAF did not mention any military casualties. The Afghan official said some civilians were also killed in the
attack, but the death toll remained unclear.

Police and ambulances rushed to the scene
near the Pul-i-Charkhi prison. Two civilian vehicles lay overturned and nearby
shop windows were shattered from the force of the explosion.

The Afghan official said U.S. troops responded to the incident.

A local shopkeeper named Jameel, who uses
only one name, says he saw two NATO vehicles leaving the prison and a car
slamming into the second one.

A claim of responsibility was issued by the
second largest Islamic militant group in Afghanistan, Hezbi Islami. .

Militants from the Afghan Taliban, the
largest insurgent group in the country, and other affiliated organizations, have
stepped up attacks in the final year of the international coalition's combat
mission in Afghanistan, seeking to
shake confidence in the Kabul government's ability to keep order.